Reinforced vascular graft

ABSTRACT

An instrument is provided for supporting a tubular vascular graft during endovascular implantation and methods for use thereof. In one embodiment, the instrument is formed from two flexible guidewires bent to each define a loop and two straight portions. In a second embodiment, the instrument is formed from two flexible guidewires bent to define outwardly-biased tines, wherein, threads are sewn to portions of the vascular graft and connected to the tines. The instrument is collapsible due to the flexibility of the guidewires used to form the instrument. In an uncollapsed state, with a length of graft material being mounted to the instrument, the loops or tines may bias the graft into a semi-expanded state with a passage being defined through the graft. An unexpanded stent is introduced into the passage of the semi-expanded graft to both further expand the graft and provide reinforcement. A distensible device is also used with the preferred method of using the invention to accomplish full circumferential expansion of the graft and stent assembly and to facilitate removal of the instrument. In a further embodiment of the invention, a bent guidewire is provided which is securely connected to the graft to act as a guide thereof. Also, a series of concentrically disposed stents can be utilized with the invention.

This application is a division of U.S. patent application Ser. No.09/148,347, filed Sep. 4, 1998, which is a continuation-in-partapplication of U.S. application Ser. No. 09/025,713, filed Feb. 18,1998, now U.S. Pat. No. 6,015,422.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to devices and methods for endovascular treatmentof blood vessel anomalies and, more particularly, for the implantationof vascular grafts.

2. Description of the Prior Art

Blood vessel anomalies, such as aneurysms, stenoses, etc., have beentreated in the prior art through surgical procedures, wherein thediseased portion of the blood vessel may be ablated and replaced with a,prosthetic member, such as shown in U.S. Pat. No. 4,938,740 to Melbin.An improvement over this technique which obviates the need for opensurgery is directed to the endovascular placement of a stent-reinforcedgraft. The stent and graft is entered into the bloodstream from a remotepuncture site, typically through the neck or femoral region, via acatheter in an unexpanded state to facilitate movement thereof throughthe blood vessel. The stent/graft assembly is aligned in the bloodvessel using techniques known by those skilled in the art such that theassembly extends between healthy portions of the blood vessel andby-passes the blood vessel anomaly. Once properly aligned, the stent andgraft are caused to expand thereby engaging axially-spaced sections ofhealthy blood vessel wall and defining an enclosed pathway for bloodflow through the anomaly. If, for example, a graft was disposed in sucha manner to by-pass an aneurysm and such aneurysm ruptured, the emplacedgraft would act as a conduit to maintain a continuous flow of bloodthrough the ruptured portion of blood vessel.

Different devices are in the prior art which allow for endovascularmovement of a stent and/or graft and expansion thereof. First, devicesexist adapted to selectively elongate and foreshorten a length oftubular graft material, resulting in a corresponding change in diameterof the graft, such as in U.S. Pat. No. 5,464,449 to Ryan et al.Alternatively, a stent and/or graft may be directly disposed on anexpandable angioplasty balloon, as shown in U.S. Pat. No. 5,554,182 toDinh et al. Finally, self-expanding stents and/or grafts are known inthe prior art which are spring-biased or formed of temperature sensitivematerial. An example of this third type of prior art is found in U.S.Pat. No. 5,562,725 to Schmitt et al.

The prior art, however, has some deficiency in providing forimplantation of a stent-reinforced graft. The mounting of the graft ontoa stent, in addition to a control mechanism or an angioplasty balloon,results in the graft defining a relatively significant outer dimension.As is readily appreciated, due to the small dimensions of blood vessellumens, it is desirable to keep the profile of all endovascular devicesto a minimum. Also, lower profile instruments are more easilymanipulated through blood vessels, than larger profile instrumentsespecially through blood vessels which may contain accumulated plaque.

It is an object of the subject invention to provide a collapsiblesupport for a vascular graft which allows for low-profile insertionthereof.

It is also an object of the subject application to provide a support formaintaining a graft in a semi-expanded state with sufficient spacewithin the graft to preferably accommodate an unexpanded stent.

SUMMARY OF THE INVENTION

The aforementioned objects are met by a frame for supporting a vasculargraft. In a first embodiment, the frame is formed from two flexibleangiographic guidewires bent to define two spaced-apart loops, the loopsbeing dimensioned to support the graft in a semi-expanded state.

The angiographic guidewires may be of any resilient type known to thoseskilled in the art which is formed to have memory, i.e., being capableof, upon deformation, generally returning to a pre-deformation shape.Each guidewire is bent to define, in a natural state, a loop and asegment with the segment including a generally straight first portionextending from the loop, and a generally straight second portionextending from the first portion and through the supported vasculargraft. The loops are formed with frangible connections, such as throughwelding, which allow for the loops to be respectively torn open uponsufficient application of force. Further, the second portions of bothguidewires are joined together along the respective lengths thereof,with the joined second portions extending through the loops of bothguidewires to define a common shaft of the instrument.

With the loops supporting the vascular graft, the loops are dimensionedto partially expand the graft circumferentially and allow for passage ofan unexpanded stent thereinto with the stent being threaded over thecommon shaft. In this manner, the stent may be introduced inside thegraft supported by the subject invention with circumferential expansionof the introduced stent further circumferentially expanding thepartially-expanded graft.

The first embodiment is preferably used in conjunction withself-expanding stents. As described below, if a self-expanding stent isutilized, a distensible device, such as a angioplasty balloon, will beintroduced separately from the stent to allow for proper removal of theinvention and implantation of the graft. Alternatively, a stent may beutilized which is not self-expanding and requires mechanical force forexpansion. In the alternative variation, the stent may be directlymounted to a distensible device, such as a angioplasty balloon.

In use of the first embodiment, a length of tubular graft material, anyresilient graft material known to those skilled in the art which isexpandable (e.g. PTFE), is mounted onto the invention with the loopsbeing in engagement with the inner surface of the graft. The graft andthe loops are then caused to be collectively collapsed with the graftbeing circumferentially compressed substantially about the common shaftand the loops being interposed between the graft and the common shaft indistorted states. Preferably, the graft and the loops are maintained inthe collapsed position by a lubricous plastic being tightly disposedabout the graft. Once collapsed, the assembly is introduced into thebloodstream and guided therethrough using techniques known to thoseskilled in the art. The graft is properly positioned in the desiredlocation with the ends of the graft being aligned with healthy portionsof blood vessel found at axially-spaced locations about the anomalywhich is being treated. Thereafter, the lubricous plastic is removedfrom the graft, thus, allowing the loops to regain memory and bias thegraft into a semi-expanded state, with a passage being defined throughthe graft.

With the graft being partially expanded, an unexpanded stent isintroduced inside of the graft to provide reinforcement for supportingthe graft. In the preferred variation of the first embodiment, aself-expanding stent is introduced inside of the semi-expanded graft bythreading and advancing the stent over the common shaft of theinvention. With the stent being aligned with the graft, the stent isallowed to expand, which causes the graft to be further expanded.Afterwards, a distensible device, such as an angioplasty balloon, isintroduced inside of the semi-expanded stent and graft assembly. Thedistensible device is caused to be expanded which, in turn, causes thestent and graft assembly to become fully expanded with the graft cominginto pressing engagement with healthy portions of the blood vessel wall.Simultaneously, the expansion of the distensible device will cause thefrangible connections used to form the loops of the invention to break,thus breaking the loops. The distensible device is then deflated andwithdrawn, and, finally, the invention is withdrawn from the bloodvessel with the portions of the guidewires which define the loops beingpulled out from between the expanded stent and expanded graft uponwithdrawal of the invention. As a result of this procedure, a fullyexpanded stent-reinforced graft is implanted at a desired location in ablood vessel.

In alternate variations of the first embodiment of the invention, threadcan be wrapped about the collapsed graft to maintain it in a closedposition. Also, a non-self-expanding stent may be utilized which isdirectly mounted onto the distensible device.

In a second embodiment of the invention, the frame is formed from twoflexible angiographic guidewires bent to define two outwardly biasedtines. A loop of thread is knotted to the end of each tine which is sewninto portions of the graft material which is to be implanted. Thethreads prevent movement of the graft relative to the frame. As with thefirst embodiment, the angiographic guidewires, may be of any resilienttype known to those skilled in the art which is formed to have memory.Each guidewire is bent to define, in a natural state, the tine extendingfrom a segment. The segments are joined to define a common shaft for theinstrument. The tines are biased so that the free ends of the tines arespaced from the common shaft of the instrument in a natural state. Also,the tines are formed with varying lengths to enable engagement of thegraft at axially-spaced locations by the instrument. The thread iscaused to engage the graft such that the movement of the graft relativeto the instrument is minimized—e.g. the thread may be sewn into portionsof the graft. The length of each thread must be less than thecircumference defined by the inner surface of the graft in an expandedstate. As such, upon expansion of the threads and the graft, the loopsdefined by the threads would rupture prior to the full circumferentialexpansion of the graft.

In use of the second embodiment, the graft is mounted to the instrumentwith the tines and threads engaging axially-spaced locations of thegraft. The tines and the graft are both caused to be collapsed, with thegraft being circumferentially compressed substantially about the commonshaft and the tines being interposed between the graft and the commonshaft in pressing engagement with the common shaft. As with the firstembodiment, lubricous plastic is preferably wrapped about the collapsedgraft to maintain it in the collapsed position. Alternatively, threadmay be wound about the graft. Once the collapsed assembly is introducedinto the bloodstream and, properly located the plastic is retracted thusexposing the graft. The bias of the tines will cause somecircumferential expansion of the graft such that the graft comes into asemi-expanded state.

The second embodiment is used in the same manner as the firstembodiment. An unexpanded self-expanding stent is preferably introducedinto the semi-expanded graft and caused to expand. Likewise, adistensible device is also introduced. Upon expansion of the distensibledevice, the stent and graft become fully expanded and the loops formedby the threads become ruptured. Thereafter, the instrument is removed.

With respect to a third embodiment of the invention, the thirdembodiment actually encompasses variations of the first two embodiments.In one variation of the third embodiment, the structure of the firstembodiment is provided, but the loops need not be formed with memory.Similarly, a second variation of the third embodiment is directed to thesame structure of the second embodiment of the invention, but the tinesneed not be biased. In either variation of the third embodiment, theloops and tines are used to simply maintain the graft in a relativelyfixed position along the common shaft of the instrument, but not formedto partially expand the graft. The loops of the structure of the firstembodiment may, through frictional engagement, maintain the position ofthe graft. Likewise, the engagement of the thread-formed loops of thesecond embodiment may also prevent movement of the graft. With respectto the third embodiment, since the graft will not be forced into asemi-expanded state, the catheter which bears the first instrumentinserted into the graft during the procedure of endovascularimplantation (either a self-expanding stent or a combination of a stentand a distensible device) will be formed with a sharpened or ramped tipwhich will allow the catheter to slip into the unexpanded graft alongwith the device mounted to the catheter. Simultaneously, the catheterwill slip through the loops of either embodiment also. The use of thethird embodiment is the same as the first two embodiments in all otherrespects.

With respect to a fourth embodiment of the invention, a system isprovided which includes a single flexible guidewire having one endconnected to a tubular graft by a thread. The end of the guidewire issecured in proximity to one end of the graft, and the guidewire is bentfrom the secured end to define a generally U-shape, with a leg portionof the guidewire extending through the graft.

The thread used to form the securement is preferably 7-0 silk thread.The thread used must be sufficiently strong to ensure securement betweenthe guidewire and the graft, but also it is desired that the thread notbe excessively strong in tensile, since the thread must be brokenendovascularly as described below. It has been found that thinnerthreads are very effective in use with the invention, since a great dealof tensile strength is not required to maintain securement between theguidewire and the graft, and thinner threads can more readily be brokenthan thicker, stronger threads.

The system of the fourth embodiment is used in conjunction with aself-expanding stent, as well as an introducer catheter, a pushercatheter, and a dilator. In use, the graft is collapsed and urged intothe lumen of the introducer catheter, along with the attached guidewire.The distal end of the introducer catheter is inserted into a patientthrough a puncture site and guided to the blood vessel anomaly which isto be treated. At the treatment site, the introducer catheter is heldstationary and the guidewire is advanced to allow for release andsubsequent expansion of the graft. The introducer catheter, which ispreferably formed with a sharpened or ramped distal tip, is thenadvanced through the expanded graft and held stationary. Theself-expanding stent is urged through the lumen of the introducercatheter through use of the pusher catheter, wherein the introducercatheter is held stationary until the self-expanding stent is initiallyreleased from the distal end thereof. Thereafter, the pusher catheter isheld in a fixed position, and the introducer catheter is slowlyretracted to allow for further release of the self-expanding stent. Asthe introducer catheter is retracted, the self-expanding stent becomesreleased within the graft. Once the self-expanding stent has been fullyreleased, the dilator, preferably having a sharpened or frustoconicaldistal tip, is advanced over the guidewire through the lumen of theintroducer catheter. The distal end of the dilator eventuallystraightens the U-shaped portion of the guidewire and eventually comesinto engagement with the thread. With the guidewire being withdrawn, thedilator is further advanced to cause a break in the thread connectingthe guidewire to the graft. Consequently, the guidewire becomes freedfrom the graft and is retracted, along with the dilator and theintroducer catheter, leaving the expanded stent and graft assembly inthe blood vessel.

As a variation of the fourth embodiment, in lieu of introducing adilator, the thread can be caused to be broken through rotation of theguidewire, wherein the thread will coil about the guidewire andeventually break.

With respect to a fifth embodiment of the invention, a system isprovided which is a variation of any of the first, second and thirdembodiments of the invention which utilize a self-expanding stent. Inthe fifth embodiment, a series of thinner stents is utilized in lieu ofa single “full size” stent. The number and strength of the thinnerstents are determined by the strength of the single stent required forthe application. The thinner stents are to be concentrically disposedwithin the graft with the thinner stents collectively generating atleast the same biasing force as the single “full size” stent to theinner surface of the graft. Through the use of a series of thinnerstents, the fifth embodiment advantageously allows for a lower profileassembly to be introduced into a patient than where a single “fullsize”, stent is used.

These and other features of the invention will be better understoodthrough a study of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the first embodiment of the invention.

FIG. 2 is a plan view of the first guidewire used to form the firstembodiment of the invention.

FIG. 2 a is a plan view of the first guidewire with the loop beingdiscontinuous to show the construction thereof.

FIG. 3 is a plan view of the second guidewire used to form the firstembodiment of the invention.

FIG. 4 is a plan view of the first embodiment of the invention with avascular graft being mounted thereto.

FIG. 5 is a plan view of the invention in collapsed state with plasticbeing wrapped thereabout.

FIG. 6 is a plan view of the invention in a collapsed state with threadbeing wrapped thereabout.

FIG. 7 is a plan view of the invention arranged with an unexpanded stentand unexpanded distensible device.

FIGS. 8-10 show schematically the use of the first embodiment toendovascularly implant a graft to by-pass an aneurysm.

FIG. 11 is a schematic of an arrangement of a variation of the firstembodiment wherein a stent is directly mounted onto a distensibledevice.

FIG. 12 is a plan view of the second embodiment of the invention.

FIG. 13 is a plan view of the first guidewire used to form the secondembodiment of the invention.

FIG. 14 is a plan view of the second guidewire used to form the secondembodiment of the invention.

FIG. 15 is a plan view of the second embodiment of the invention with avascular graft being mounted thereto.

FIG. 16 is a side view of the second embodiment of the invention with avascular graft being mounted thereto.

FIG. 17 is a plan view of the third embodiment of the invention arrangedwith an unexpanded stent.

FIG. 18 is a plan view of the fourth embodiment of the invention.

FIGS. 19-23 show schematically the use of the fourth embodiment toendovascularly implant a graft to by-pass an aneurysm.

FIG. 24 shows schematically a variation of using the fourth embodimentwhere the thread is broken by rotating the guidewire.

FIG. 25 is a schematic of the fifth embodiment of the invention.

FIG. 26 is a plan view of the fifth embodiment showing a series ofstents being concentrically disposed within a graft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring generally to FIGS. 1-11, the first embodiment of the inventionis shown. In FIG. 1, an instrument 10 is depicted for supporting avascular graft during endovascular implantation thereof. The instrument10 is generally comprised of a first and a second flexible guidewire 12and 14, respectively, with each guidewire being formed to generallydefine respectively loops 16 and 18 and a common shaft 20.

The guidewires 12, 14 are to be formed of any resilient type of materialknown to those skilled in the art which is formed to have memory, i.e.,being capable of, upon deformation, generally returning to apre-deformation shape. Referring to FIG. 2, the first guidewire 12 isbent to define the loop 16 and a segment 22 extending from the loop 16.The first guidewire 12 is formed from one continuous length of guidewirewith a predetermined length of guidewire extending from one end 24defining the loop 16. The segment 22 includes a first portion 26 and asecond portion 28. FIG. 2 a depicts the first guidewire 12 with the loop16 not being closed to illustrate the formation of the first guidewire12. As shown in FIG. 2 a, the first guidewire 12 is bent from the firstend 24 to generally define the arcuate shape of the loop 16, furtherbent about the corner 30 to define the first portion 26, and furtherbent about corner 32 to define the second portion 28. The corner 32 ispreferably rounded, not sharp. The loop 16 is closed with the first end24 being frangibly connected to the corner 30. The strength of thefrangible connection is as described below.

The second guidewire 14 is generally formed in the same manner as thefirst guidewire 12. Specifically, as shown in FIG. 3, the secondguidewire 14 is formed from a continuous length of guidewire bent todefine the loop 18, and a segment 34, which includes a first portion 36and a second portion 38. Similar to the first guidewire 12, the secondguidewire 14 is bent to define the loop 18 from one end 40, about acorner 42 to define the first portion 36, and about a corner 44 todefine the second portion 38. The corner 44 is preferably rounded.Again, similar to the loop 16 of the first guidewire 12, the loop 18 isclosed due to a frangible connection between the end 40 and the corner42, wherein the strength of the frangible connection is also discussedbelow.

The instrument 10 is formed by joining the second portion 28 of thefirst guidewire 12 and the second portion 38 of the second guidewire 14,with the corners 32 and 44, respectively, of the guidewires beingaligned. The joined first portions 28 and 38 collectively define thecommon shaft 20 of the instrument 10, and, the corners 32 and 44collectively define a tip 45 of the instrument 10. As shown in FIG. 1,the common shaft 20 is disposed to extend through both of the loops 16and 18. The length of the common shaft 20, as measured extending fromthe tip 45, is determined by the length necessary to properly positionand manipulate the instrument 10 from a location external of thepuncture site, as described below. As is readily apparent, the length ofthe common shaft 20 is determined by the respective lengths of thesecond portions 28 and 38.

The loops 16 and 18 are preferably elliptically formed, but may also beformed to define other shapes. Also, the loops 16 and 18 are preferablyformed to generally define the same dimensions. In forming theinstrument 10, however, it is desired that the loops 16 and 18 belocated at axially-spaced locations relative to the common shaft 20. Tothis end, in forming the first guidewire 12, the length of the firstportion 26 is defined such that the loop 16 is located a distance “x”from the corner 32, and the loop 18 of the second guidewire 14 is formeda distance “y” from the corner 44, with the distance “y” being greaterthan the distance “x”. The actual spacing between the loops 16 and 18 isdependent upon the length of the vascular graft which is to be supportedby the instrument 10. Preferably, the loops 16 and 18 are located inproximity to the ends of the vascular graft.

It should be noted that although the first embodiment is disclosed asbeing formed with two loops 16, 18, any number of loops could be used.It is preferred, however, that the loops be located to ensure that atleast the end of the vascular graft into which the stent is to beinserted, as described below, will be biased open.

It should also be noted that although the respective first portions 26and 36 of the guidewires 12 and 14 are shown to be generally straight,the second portions 26 and 36 need only extend between the respectivecorners 32 and 44 to the respective corners 30 and 40 and need not beformed to be generally straight. As such, the first portions 26 and 36extend continuously angularly relative to the common shaft 20 betweenthe respective corners 32 and 44 to the respective corners 30 and 40.

FIG. 4 shows a length of tubular vascular graft 44 mounted onto theinstrument 10, with the loops 16, 18 being in pressing engagement withthe inner surface 46 of the graft 44. The vascular graft 44 may be ofany resilient type known to those skilled in the art. The memory of theloops 16 and 18 cause the graft 44 to be at least partially expandedsuch that, as shown in FIG. 4, a passage is formed through the graft 44about the common shaft 20 which is large enough to accommodate theunexpanded stent (discussed below) intended to be used with theinstrument 10. In natural states, as shown in FIGS. 2 and 3, the loops16 and 18 must be formed with dimensions which are at least as great asthe dimensions required to allow passage of the unexpanded stent intothe graft 44—i.e. the loops 16, 18 must be dimensioned such that thememory of the loops 16, 18 will at least provide for sufficientexpansion of the graft 44 to allow for passage of the unexpanded stentinto the graft 44.

To facilitate implantation of the graft 44 in a desired location in ablood vessel, the instrument 10 and graft 44 are collectively caused tobe circumferentially collapsed, about the common shaft 20 as shown inFIGS. 5-6. Referring specifically to FIG. 5, the collective assembly ofthe instrument 10 and the graft 44 can be maintained in a collapsedposition by disposing a lubricous plastic overwrap 48 tightly about theouter surface of the graft 44. Any lubricous plastic known to thoseskilled in the art, such as hydrophilic plastics, which is sufficientlystrong to resist outward circumferentially-generated pressure due to thetendency of the loops 16 and 18 to regain memory may be utilized. Thelubricity of the plastic 48 allows for easy removal thereof from thegraft 44 by simply urging the plastic 48 rearwardly, using techniquesknown in the prior art, in a direction along the axis of the commonshaft 20, thus causing it to slip off the graft 44. Alternatively,referring to FIG. 6, a thread 50 may be wound about the collapsedinstrument 10 and the graft 44 with the thread 50 having sufficientlength to have one end 52 extend externally from the puncture site. Theother end 54 of the thread 50 is knotted to a point along theintermediate length of the thread 50 such that a jerk of the thread 50at the end 52 will cause the knot formed by the end 54 to break and theentire thread 50 can be withdrawn. In FIG. 6, the thread 50 is shown asbeing passed over the tip 45 of the instrument 10, however, the thread50 may be wound about the graft 44 in other configurations.

FIG. 7 shows a preferred arrangement for using the instrument 10 inimplanting the graft 44. Referring to FIG. 7 and going from the left tothe right of the figure, the device 10 is shown having the graft 44mounted thereto, the graft 44 and the instrument 10 being bothcollapsed. Although not shown, a tubular stiffener, known in the priorart, is preferably disposed over the common shaft 20, extending from thetip 45 to the free end of the common shaft 20. The stiffener is disposedadjacent the common shaft 20 to provide rigidity thereto. The lubricousplastic 48 (shown to be transparent) is wrapped about the collapsedgraft 44, in a similar manner as that shown in FIG. 5. In contrast toFIG. 5, the plastic 48 extends beyond the graft 44 in a rightwarddirection to encapsulate further elements. An unexpanded self-expandingstent 54 is located to the right of the graft 44 which is mounted to acatheter 56. Any type of self-expanding stent, such astemperature-sensitive stents, may be used with the invention. Thecatheter 56 is thread onto the common shaft 20 so that the stent 54 isslidable along the length thereof. To the right of the stent 54 islocated an unexpanded distensible device 58, preferably, an angioplastyballoon. The distensible device 58 is mounted onto a catheter 60, whichin turn, is threaded onto the catheter 56. The lubricous plastic 48 isextended over the stent 54 and the distensible device 58, in addition tothe graft 44, to not only maintain the graft 44 in a collapsed position,but also prevent expansion of the stent 54 and the distensible device58. It can be readily appreciated that the low-profile arrangement shownin FIG. 7 allows for relative movement of the graft 44, the stent 54 andthe distensible device 58 relative to one another. To allow for suchindependent movement during use, the common shaft 20, the catheter 56and the catheter 60 must be formed with lengths extending in a rightwarddirection sufficiently to allow for a physician to manipulate thevarious devices externally of the puncture site.

FIGS. 8-10 schematically depict an exemplary use of the invention. Aportion of a blood vessel BV is shown in which an aneurysm A is formedwhich is to be by-passed by a stent-reinforced vascular graft. AlthoughFIGS. 8-10 show an application of the invention with respect to theaneurysm A, the invention can be used to treat other blood vesselanomalies which can be treated through the endovascular implantation ofa stent-reinforced vascular graft. In the first stage of use, thelow-profile assembly shown in FIG. 7 is introduced into the blood vesselBV from a remote puncture site. Using techniques known by those skilledin the art, such as fluoroscopy, the instrument 10 is aligned to by-passthe aneurysm A such that the graft 44 extends between axially-spacedhealthy portions of the blood vessel BV, generally designated by thenumeral 62. Once aligned, the lubricous plastic 48 is caused to beretracted relative to the vascular graft 44, thus exposing the vasculargraft 44. Consequently, the loops 16 and 18 (not shown) regain somememory and bias the graft 44 into a semi-expanded state, which issimilar to the state shown in FIG. 4.

Referring to FIG. 9, the stent 54 is then advanced over the common shaft20 into the semi-expanded graft 44 with the lubricous plastic 48 beingthereabout. Afterwards, the plastic 48 is retracted to expose the stent54, thus allowing the stent 54 to circumferentially self-expand withinthe loops 16 and 18 and the graft 44. The strength of the frangibleconnections used to form the loops 16 and 18 is determined by the degreeof force which may be generated by the expansion of the stent 54.Preferably, the loops 16 and 18 are provided with frangible connectionswhich can withstand the circumferential expansion of the stent 54, butwhich can be broken by expansion of the distensible device 58.Alternatively, although not desired, the loops 16 and 18 may be formedwith frangible connections which can be ruptured by the expansion of thestent 54, thus obviating the need for the distensible device 58. Itshould be noted, however, that with such an alternative construction,the frangible connections would be weaker than in the preferredembodiment and may be susceptible to failure. Further, if no distensibledevice is to be utilized, the stent 54 must be capable of fullyexpanding the graft 44. If the stent 54 is capable of generating asubstantial degree of force due to expansion and fully expanding thegraft 44, thus allowing for stronger frangible connections, thealternative embodiment could become a desirable alternative.

In the first embodiment, the stent 54 must sufficiently expand withinthe loops 16, 18 so that a passage is defined therethrough which issufficient to accommodate the unexpanded distensible device 58.Thereafter, the distensible device 58 is exposed by the plastic 48 andadvanced into the passage defined by the stent 54. Using techniquesknown by those skilled in the art, the distensible device 58 is cause toexpand, simultaneously causing the full expansion of the graft 44 andthe stent 54. Consequently, the outer surface of the graft 44 comes intopressing engagement with the healthy portions 62 of the blood vessel BV.The expansion of the distensible device 58 also causes rupture of thefrangible connections used to respectively form the loops 16 and 18.Upon rupture of the frangible connections, as shown in FIG. 10, theportions of the first and second guidewires 12 and 14 which extend fromthe respective ends 24 and 40 to form the loops 16 and 18, respectively,are interposed between the expanded stent and the expanded graft 44. Thecommon shaft 20 is then retracted thus causing the first and secondguidewires 12 and 14 to be drawn from between the stent 54 and the graft44 and through the catheter 60 which supports the expanded distensibledevice 58. Finally, the distensible device 58 is deflated and withdrawn,leaving the expanded stent-reinforced graft 44 in the blood vessel BV.

In a variation of the first embodiment, a non-self-expanding stent 64may be utilized with the instrument 10. The stent 64 may be directlymounted onto the distensible device 58 which relies upon the distensibledevice 58 for force to facilitate expansion thereof. In use, theinstrument 10 and the graft 44 may be maintained in a collapsed statethrough either the use of the lubricous plastic 48 or the thread 50.Similar to the above-described procedure, the graft 44 is alignedrelative to the aneurysm A which is to be treated and caused to besemi-expanded. The graft 44 must be sufficiently expanded to facilitateentry of the combined stent 64 and distensible device 58 assembly. Thestent 64 is advanced into the graft 44, along with the distensibledevice 58, through the manipulation of the catheter 60. Thereafter, thedistensible device 58 is caused to expand, with simultaneous expansionof the stent 64, the graft 44 and the rupturing of the frangibleconnections used to form the loops 16 and 18. As described above, theinstrument 10 and the distensible device 58 are then withdrawn.

Referring generally to FIGS. 12-16, the second embodiment of theinvention is shown therein. An instrument 66 is provided for supportingthe graft 44 during an endovascular implantation thereof. The instrument66 is formed from first and second flexible guidewires 68, 70, eachbeing bent to define outwardly-biased tines 72, 74.

As more clearly shown in FIG. 13, the first guidewire 68 is formed fromone continuous length of guidewire which is bent to define the tine 72and a segment 76. The tine 72 and the segment 76 are joined at corner78. The corner 78 is preferably rounded. The first guidewire 68 isformed from a naturally resilient material which generates a bias aboutthe corner 78 to cause a free end 80 of the tine 72 to be spaced fromthe segment 76 in a natural state. As shown in dashed lines in FIG. 13,the corner 78 provides a hinged connection about which the tine 72 maypivot relative to the segment 76.

Referring to FIG. 14, the second guidewire 70 is shown, which isbasically shaped and constructed in the same fashion as the firstguidewire 68. Specifically, the second guidewire 70 is formed with thetine 74 being connected to a segment 82 about a corner 84. The corner 84is preferably rounded. As with the construction of the first guidewire68, the tine 74 is formed with a free end 86 which is biased to bespaced from the segment 82.

The instrument 66 is formed by joining the segments 76 and 82 to definea common shaft 88. In forming the common shaft 88, the corners 78 and84, respectively, are aligned to form a tip 90 of the instrument. Asdescribed above, and with respect to the first embodiment, and referringto FIG. 12, the common shaft 88 must be provided with a sufficientlength in the rightward direction which would allow a physician tooperate the instrument 66 from a location external the puncture site.The length of the common shaft 88 is a direction function of the lengthsof the segments 76 and 82.

As with the first embodiment of the invention, it is desired that theinstrument 66 engage axially-spaced apart locations of the graft 44. Toachieve this end, the tines 72 and 74 must be formed of differentlengths. As shown in FIG. 13, the tine 72 is formed to define a distance“a” from the corner 78 to the free end 80. In a similar manner, as shownin FIG. 14, the tine 74 is formed to define a distance “b” from thecorner 84 to the free end 86. It is preferred that the distance “b” begreater than the distance “a” to ensure engagement at axially-spacedlocations of the graft 44. The distance “b”, however, could equal thedistance “a”. Also, in forming the instrument 66, the tines 72, 74 arepreferably oriented relative to the common shaft 88 to extend inopposing directions therefrom. Referring to FIG. 16, a side view of theinstrument 66 is shown with the graft 44 being mounted thereon. As canbe seen, the tines 72 and 74 are disposed to be at diametrically opposedlocations relative to the common shaft 66.

FIG. 15 shows the graft 44 being mounted to the instrument 66 The freeends 80, 86, respectively, of the tines 72, 74 engage the inner surface46 of the graft 44 at axially-spaced location. The bias applied to thetines 72 and 74 urges the free ends 80, 86 outwardly from the commonshaft 66, and as a result, cause the graft 44 to partially expand. Aswith the first embodiment, it is desired that the graft 44 besufficiently expanded to allow for entry of an unexpanded stentthereunto. Thus, the free ends 80, 86 must respectively be spaced fromthe common shaft 88 a distance which is at least as great as half of theouter diameter of the unexpanded stent—i.e. the tines 72, 74 must beformed such that the bias applied to the tines 72, 74 will at leastprovide for sufficient expansion of the graft 44 to allow for passage ofthe unexpanded stent into the graft 44.

To prevent movement of the graft 44 relative to the common shaft 66, alength of thread 92, 94 is secured to each of the free ends 80 and 86which generally defines the shape of a loop. Additionally, the threads92, 94 are sewn through portions of the graft 44, as shown in FIG. 15.The threads 92, 94 are to be secured to the free ends 80, 86 with bothends of each of the threads 92, 94, respectively engaging the tine 72,74. The threads 92, 94 are to be secured so that one end thereon willdisconnect from the tine 72, 74 upon expansion of the distensible device58, but not the stent 54.

Although FIG. 15 shows the graft 44 to have a generally cylindricalshape in a semi-expanded state, the graft 44 may not necessarily havesuch a shape. Referring to FIG. 16, prior to expansion, the graft 44 mayhave pleats or folds formed thereon due to its semi-expanded state. FIG.16 shows the thread 92 formed to define an elliptical loop secured tothe tine 72 and passing in and out of the graft 44 in a sewnconfiguration. The dashed lines in FIG. 16 represent the graft 44 in afully expanded state. The graft 44 in a fully expanded state will definean inner radius “r”. For use of the invention as described below, thelength of the threads 92, 94 must be less than the circumference definedby the fully expanded graft 44. Stated algebraically, the length of thethreads 92, 94, respectively, must be less than 2πr.

It can be appreciated that although the description of the secondembodiment set forth above is directed to the use of two tines 72, 74and two lengths of thread 92, 94 any number of tines and/or threads maybe used. Also, the tines 72, 74 need not be formed to be straight, butonly having an end or portion for engaging the graft 44.

It should also be noted that although the tines 72, 74 are shown toextend into the graft 44, the tines 72, 74 may likewise be disposed tobe outside of the graft 44. In this variation, the tines 72, 74 actuallypull open the graft 44 to the semi-expanded state. This variation mustbe used cautiously since the tines 72, 74 will contact directly theblood vessel.

The second embodiment of the invention is used in the same arrangementand in the same manner as the first embodiment. Once the loops definedby the threads 92, 94 are ruptured, the common shaft 66 may be advancedso that the tines 72, 74 pull the threads 92, 94, thus ensuring thethreads 92, 94 are fully withdrawn from the graft 44. Afterwards, eitherthe catheter 60, which supports the distensible device 58, may beadvanced over or the instrument 66 may be retracted into the catheter 60and the instrument 66 may be removed. The lumen of the catheter 60 mustbe sufficiently dimensioned to capture the free ends 80 and 86 of thetines 72 and 74, which would be in natural states. The second embodimentmay also be used with the non-self-expanding stent 64.

FIG. 17 is directed to a third embodiment of the invention. The thirdembodiment encompasses variations of the first two embodiments. Withrespect to the third embodiment, the structure of the instruments as setforth above remains the same. However, the loops 16 and 18 of theinstrument 10 of the first embodiment, and the tines 72 and 74 of theinstrument 66 of the second embodiment need not be formed with memory orbias. Instead, the third embodiment merely functions to maintain thegraft 44 in a relatively fixed location along the instrument but notprovide any impetus to cause the graft 44 to expand. Specifically, withrespect to the structure of the first embodiment, the frictionalengagement between the structure of the loops 16, 20 and the segments22, 34 is relied upon. With respect to the structure of the secondembodiment, the stitching of the threads 92 and 94 are relied upon tomaintain the graft 44 in a relatively fixed position.

Since however the graft 44 will not be forced into a semi-expandedstate, a catheter must be provided having a sharpened or ramped end 96.FIG. 17 depicts an exemplary illustration of the third embodiment of theinvention. The graft 44 is shown to be supported by the instrument 10and the stent 54 is shown to be supported by the catheter 56. Thecatheter 56 is provided with the sharpened tip 96. In use, as describedabove with respect to the first and second embodiments, upon introducingthe stent 54 into the graft 44, the tip 96 would be forced into thegraft 44 and cause expansion thereof. Further advancement of the tip 96will cause the tip 96 to slip under the loops 16, 18 (not shown) withthe catheter 56 and the stent 54 following. If variations of theembodiments are used and the non-self expanding stent 64 is utilized,the catheter bearing the stent 64 is formed with the tip 96.

FIGS. 18-23 depict a fourth embodiment of the invention. Specifically,as shown most clearly in FIG. 18, an instrument 98 is provided which isformed by a single resilient guidewire 100. The guidewire 100 has adistal end 102 to which is attached one end 104 of a length of thread106. The guidewire 100 is bent from the distal end 102 to define anU-shaped portion 108, with a leg 110 extending therefrom to a proximalend 112 of the guidewire 100. The guidewire 100 may be formed of anyflexible guidewire material known in the prior art.

The instrument 98 is used in conjunction with the graft 44. The thread106 has a second end 114 which is knotted, such as with a suture, inproximity to an end 116 of the graft 44. Due to the resiliency of thegraft 44, the instrument 98 has a natural state as shown in FIG. 18.

It is preferred that the thread 106 be thin, such as 7-0 silk thread.The thread 106 functions to maintain securement between the guidewire100 and the graft 44 during an endovascular procedure. It has been foundthat a minimal amount of tensile strength in the thread 106 is needed tomaintain the connection between the guidewire 100 and the graft 44. Byutilizing relatively thin thread material for the thread 106, the thread106 can advantageously be easily broken as described below.

The instrument 98 is used in conjunction with the self-expanding stent54, described above, as well as with an introducer catheter 118, apusher catheter 120, and a dilator 122. FIGS. 19-23 depict an exemplaryprocedure using the fourth embodiment of the invention. In particular,FIGS. 19-23 depict the endovascular placement of the graft 44 into theblood vessel BV to by-pass the aneurysm A. As with other embodiments ofthe invention, the instrument 98 can be used to treat other blood vesselanomalies.

In use, the instrument 98 is collapsed and inserted into a lumen 124 ofthe introducer catheter 118. The introducer catheter 118 is insertedthrough a puncture site (not shown) with a distal tip 126 leading theway. The distal tip 126 is preferably sharpened or ramped, as shown inthe Figures. Using techniques known by those skilled in the art, theintroducer catheter 118 is guided through the blood vessel network intothe blood vessel BV which contains the aneurysm A. The distal tip 126 ofthe introducer catheter 118 is aligned to ensure the graft 44 willengage the healthy portions 62 of the blood vessel BV which surround theaneurysm A at axially-spaced locations. With the distal tip 126 beingproperly located, the introducer catheter 118 is securely held inposition, and the instrument 98 is advanced out of the lumen 124. Uponrelease, the graft 44 expands to its natural state.

Thereafter, the introducer catheter 118 is advanced with the instrument98 being held in a fixed position. The provision of the distal tip 126being either sharpened or ramped facilitates the passage of theintroducer catheter 118 through the graft 44. As shown in FIG. 20, thedistal tip 126 is advanced to be slightly beyond the graft 44. It isdesired that the distal tip 126 not engage the U-shaped portion 108 ofthe guidewire 100. Subsequently, the self-expanding stent 54 is urgedthrough the lumen 124 of the introducer catheter through the use of thepusher catheter 120. It should be noted that both the stent 54 and thepusher catheter 120 are threaded over the leg 110 of the guidewire 100.During this operation, both the instrument 98 and the introducercatheter 118 are held stationary. The self-expanding stent 54 is urgedthrough the introducer catheter 118 until a distal end 128 of the stent54 is released from the introducer catheter 118. Due to theself-expanding nature of the stent 54, the released portion of the stent54, extending from the distal end 128, expands upon release. Once thedistal end 128 is released, the pusher catheter 120 along with theinstrument 98 are both held rigidly.

Referring to FIG. 21, the introducer catheter 118 is then retracted.With the distal end 128 of the stent 54 having been expanded, the distalend 128 applies circumferential pressure against the wall of the bloodvessel BV. As the introducer catheter 118 is retracted, thecircumferential pressure generated by the distal end 128 holds the stent54 in a fixed position along with the pusher catheter 120. Consequently,the retraction of the introducer catheter 118 causes a continuousrelease of the stent 54 until eventually a proximal end 130 of the stent54 is released. As shown in FIG. 22, the complete release of the stent54 results in entire circumferential expansion thereof. It is preferredthat the axial length of the stent 54 be greater than the axial lengthof the graft 44. The stent 54 generates circumferential pressure whichpresses the graft 44 against the healthy portions 62 of the blood vesselBV.

Thereafter, the pusher catheter 120 is retracted, and the dilator 122 isthreaded over the leg 110 of the guidewire 100 and passed through thelumen 124 of the introducer catheter 118. The dilator 122 is formed witha tip 132 which is preferably tapered or frustoconically-shaped. Thedilator 122 is advanced until it straightens both the U-shaped portion108 of the guidewire 100 and the thread 106. As is readily apparent,upon expansion of the stent 54, the portion of the thread 106 which isknotted to the graft 44 is interposed between the graft 44/the stent 54and the wall of the blood vessel BV. The circumferential pressuregenerated by the stent 54, described above, maintains the thread 106 ina fixed position, in addition to the graft 44. With the guidewire 100being withdrawn, the dilator 122 is caused to further advance, resultingin tautness in the guidewire 100 and the thread 106. With continuedadvancement of the dilator 122 and simultaneous withdrawal of theguidewire 100, the thread 106 is broken, thus destroying the connectionbetween the guidewire 100 and the graft 44. As mentioned above, it isdesired that the thread 106 be weak, so as to define the “weak link” inthe instrument 98. With reference to FIG. 23, the thread 106, uponfailure, may be broken into two different pieces 106A, 106B. Finally,the guidewire 100 is retracted, along with the dilator 122 and theintroducer catheter 118. As a result of this procedure, the graft 44 isimplanted in the blood vessel BV to by-pass the aneurysm A.

As a variation of using the fourth embodiment, the thread 106 may bebroken by rotating the guidewire 100. Due to rotation of the guidewire100, the thread 106 may coil onto the guidewire 100, as shownschematically in FIG. 24, or the rotation of the guidewire 100 willcause excessive extension of the guidewire 106 and breakage thereof.

A fifth embodiment of the invention is provided which can be applied toany of the first, second, and third embodiments described above whichutilize a self-expanding stent. In forming any of the first, second, andthird embodiments with a self-expanding stent, it has be found that thethickest element of the instrument is the unexpanded stent. As such, thethickness of the unexpanded stent is the limiting factor in attemptingto achieve the lowest profile of an instrument. To further reduce theprofile of the instruments described above, a series of thinner stentsis used to replace the single “full size” stent, used respectively witheach of the instruments described above.

For illustrative purposes, the fifth embodiment is described withreference to the first embodiment, but is equally applicable to thesecond and third embodiments. In particular, as shown in FIG. 25, aseries of stents 54A, 54B are disposed on the catheter 56, in place ofthe single stent 54 described above. The number and the size of theseries of stents 54A, 54B is determined by the biasing force created bythe single stent 54. In other words, the single stent 54 is considered a“full size” stent since it is sized to singularly apply sufficientbiasing force to support the graft 44. With the fifth embodiment, the“full size” stent 54 is replaced by the series of stents 54A, 54B,wherein each of the stents 54A, 54B has a thickness “t”. The thickness“t” of the stents 54A, 54B is selected to be smaller than the thicknessof the “full size” stent 54, thus reducing the profile of theinstrument. However, because of the smaller thickness “t”, the stents54A, 54B inherently are weaker and are not capable of generating thesame circumferential biasing force as the “full size” stent 54. In usingthe fifth embodiment of the invention, the series of stents 54A, 54B aresequentially introduced inside of the graft 44, with each of the stents54A, 54B independently self-expanding. To facilitate expansion of thestents 54A, 54B, by using the instrument 10 of the first embodiment ofthe invention, the lubricous plastic 48 (not shown) is retracted toindividually expose each of the stents 54A, 54B within the graft 44. Thesecond stent 54B will not be exposed by the lubricous plastic 48 untilthe first stent 54A is fully expanded within the graft 44. As a result,the series of stents 54A, 54B are concentrically disposed within thegraft 44 as shown in FIG. 26. Although each of the stents 54A, 54B isindividually weaker than the “full size” stent 54, by concentricallydisposing the stents 54A, 54B within the graft 44, it is intended thatthe stents 54A, 54B collectively generate a circumferential biasingforce which is equal to or greater than the “full size” stent 54.Accordingly, the same or greater circumferential biasing force isapplied to the graft 44, and the overall profile of the instrument isadvantageously decreased.

As is readily apparent, numerous modifications and changes may readilyoccur to those skilled in the art, and hence it is not desired to limitthe invention to the exact construction and operation as shown anddescribed, and accordingly all suitable modification equivalents may beresorted to falling within the scope of the invention as claimed.

What is claimed is:
 1. A combination comprising: a tubular graft havinga longitudinal axis and a graft inner surface encircling saidlongitudinal axis, said graft inner surface defining an inner passagewhich extends through said graft; a tubular first stent having firstinner and outer surfaces, said first stent being disposed within saidinner passage with said first outer surface engaging said graft innersurface; and a second stent having second inner and outer surfaces, saidsecond stent being disposed within said first stent with said firstinner surface engaging said second outer surface, wherein said tubulargraft, said first stent, and said second stent are concentricallydisposed about said longitudinal axis.
 2. A combination as in claim 1,wherein said first and second stents are self-expanding stents.